1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a thin film transistor and method for fabricating the same for facilitating charge transport between source and drain and reducing an operating gate voltage.
2. Discussion of the Related Art
A thin film transistor formed with an amorphous silicon layer has been widely used as a switching device of a liquid crystal display and a linear image sensor. A thin film transistor is a field effect transistor that has a metal-insulator-semiconductor (MIS) structure. Thus, it is preferable to form the thin film transistor in self-alignment similar to a conventional MOS transistor. This is because, in this way, it is possible to reduce the parasitic capacitance and simplify photolithography.
A conventional method for fabricating a thin film transistor will be explained below with reference to FIGS. 1a and 1b. As shown in FIG. 1a, a conductive layer is deposited on a transparent insulating substrate 1, and patterned to form a gate electrode 2. Then, a gate insulating layer 3 is deposited on the overall surface of the substrate. An amorphous silicon layer 4 is formed on the gate insulating layer 3. An impurity-doped semiconductor layer 5 is deposited on the amorphous silicon layer 4.
As shown in FIG. 1b, a metal is deposited on the impurity-doped semiconductor layer 5, and patterned to form source and drain electrodes 6. A predetermined portion of the impurity-doped semiconductor layer 5 is selectively etched using the source and drain electrodes 6 as a mask. Then, a passivation layer 7 is deposited and selectively etched to form a contact hole which exposes a portion of the source or the drain electrode 6. A transparent conductive layer is deposited on the overall surface of the substrate and patterned to form a pixel electrode 8. The pixel electrode 8 is connected to the source or the drain electrode 6 through the contact hole, and thus, completing the thin film transistor.
In the above mentioned conventional method, an ohmic contact layer can be made of silicide. In this case, instead of depositing an impurity doped semiconductor layer, reaction of the amorphous silicon layer 4 with the metal forming the source and drain electrodes 6 can be utilized to form the ohmic contact layer.